Hard disk drive transducing heads, including magneto-resistive (MR) heads, can provide an asymmetric output for a variety of reasons well known to ordinarily skilled artisans. Such reasons include, but are not limited to age, temperature, thermal asperity, current changes, and the like. When an output is asymmetric, the output waveform, desirably substantially sinusoidal, can have a positive portion of the waveform that is more substantial than a negative portion thereof (or vice versa).
Various asymmetry correction approaches have been tried over the years, including providing second order and/or third order corrections, or exponential corrections, or corrections which include a modulus function. One deficiency in these approaches is their validity extends only within a relatively limited range of unsaturated states of the head. Outside of that limited range, the results tend to diverge, and are less desirable.
FIGS. 1a-1c are sample saturation curves that are plots of resistance as a function of magnetic flux. There is a portion of these curves, in the vicinity of a value Ibias, that is substantially linear. Heading in either direction on these curves away from the value Ibias, the curves have nonlinear characteristics that can be modeled in different ways. The areas on these curves outside of the outermost circles correspond to saturated states. In FIG. 1a, the area around Ibias is modeled using a purely linear function such as y=αx. As can be seen in FIG. 1a, the linear approximation works in a portion, but not in all of the unsaturated region.
FIG. 1b shows the same curve, this time with a model based on an exponential or second/third order function such as y=αxn. Again, while the model holds through part of the unsaturated region, it does not hold throughout. Finally, FIG. 1c shows the same curve again, this time with a model based on a modulus function such as y=α|x|+x, where a dark dot shows a change (break point) in the slope of the line based on the modulus function. As can be seen, once again, while this model holds through part of the unsaturated region, it does not hold throughout.
In view of this and other deficiencies, it would be desirable to have an asymmetry correction system which provides a valuable approximation to an appropriate asymmetry correction over a wider range.